My problem is that I am trying to create a solid part from an assembly of parts that fit together with a gap and have intricate hollowed out interiors. To do this I decided to seal off the gaps between the parts and create cavities using the cavity feature that only contains the outer portion. After that I will create the positive cavity from the two negative exterior parts. I already succeeded in getting the top portion to work, however the bottom portion is not working. It is not working, because it is not separating the intricate interior from the outside, thus not allowing me to select only the external body after using cavity. I have searched all around with section and I cannot find an area where the internal and external solids touch.
So my question is: how can I find the area where the internal and external solids meet so that I can seal it? Or is there an easier way to create a the solid body part?